Innervation of the mammary gland. A histochemical study in the rabbit

Progress in cancer neuroscience

Cancer of the central nervous system (CNS) can crosstalk systemically and locally in the tumor microenvironment and has become a topic of attention for tumor initiation and advancement. Recently studied neuronal and cancer interaction fundamentally altered the knowledge about glioma and metastases, indicating how cancers invade complex neuronal networks. This review systematically discussed the interactions between neurons and cancers and elucidates new therapeutic avenues. We have overviewed the current understanding of direct or indirect communications of neuronal cells with cancer and the mechanisms associated with cancer invasion. Besides, tumor-associated neuronal dysfunction and the influence of cancer therapies on the CNS are highlighted. Furthermore, interactions between peripheral nervous system and various cancers have also been discussed separately. Intriguingly and importantly, it cannot be ignored that exosomes could mediate the "wireless communications" between nervous system and cancer. Finally, promising future strategies targeting neuronal-brain tumor interactions were reviewed. A great deal of work remains to be done to elucidate the neuroscience of cancer, and future more research should be directed toward clarifying the precise mechanisms of cancer neuroscience, which hold enormous promise to improve outcomes for a wide range of malignancies.

The neuroscience of cancer

The nervous system regulates tissue stem and precursor populations throughout life. Parallel to roles in development, the nervous system is emerging as a critical regulator of cancer, from oncogenesis to malignant growth and metastatic spread. Various preclinical models in a range of malignancies have demonstrated that nervous system activity can control cancer initiation and powerfully influence cancer progression and metastasis. Just as the nervous system can regulate cancer progression, cancer also remodels and hijacks nervous system structure and function. Interactions between the nervous system and cancer occur both in the local tumour microenvironment and systemically. Neurons and glial cells communicate directly with malignant cells in the tumour microenvironment through paracrine factors and, in some cases, through neuron-to-cancer cell synapses. Additionally, indirect interactions occur at a distance through circulating signals and through influences on immune cell trafficking and function. Such cross-talk among the nervous system, immune system and cancer-both systemically and in the local tumour microenvironment-regulates pro-tumour inflammation and anti-cancer immunity. Elucidating the neuroscience of cancer, which calls for interdisciplinary collaboration among the fields of neuroscience, developmental biology, immunology and cancer biology, may advance effective therapies for many of the most difficult to treat malignancies.

The tumor-nerve circuit in breast cancer

It is well established that innervation is one of the updated hallmarks of cancer and that psychological stress promotes the initiation and progression of cancer. The breast tumor environment includes not only fibroblasts, adipocytes, endothelial cells, and lymphocytes but also neurons, which is increasingly discovered important in breast cancer progression. Peripheral nerves, especially sympathetic, parasympathetic, and sensory nerves, have been reported to play important but different roles in breast cancer. However, their roles in the breast cancer progression and treatment are still controversial. In addition, the brain is one of the favorite sites of breast cancer metastasis. In this review, we first summarize the innervation of breast cancer and its mechanism in regulating cancer growth and metastasis. Next, we summarize the neural-related molecular markers in breast cancer diagnosis and treatment. In addition, we review drugs and emerging technologies used to block the interactions between nerves and breast cancer. Finally, we discuss future research directions in this field. In conclusion, the further research in breast cancer and its interactions with innervated neurons or neurotransmitters is promising in the clinical management of breast cancer.

Many Voices in a Choir: Tumor-Induced Neurogenesis and Neuronal Driven Alternative Splicing Sound Like Suspects in Tumor Growth and Dissemination

Simple Summary

Significant progress has recently been made in understanding the role of the neuronal system in cancer biology, in many solid tumors such as prostate, breast, pancreatic, gastric and brain cancers. Solid tumors and the nervous system appear to influence each other’s development both directly and indirectly. A recurring element in such interactions is constituted by nerve-related substances such as neurotransmitters and neurotrophins, to which the first part of the current review is devoted. The second part of the review focuses on the potential role played by alternative splicing in cancer progression associated with neural signaling. Alternative splicing is the process where pre-mRNA is cut and re-ligated in different ways to give rise to multiple protein isoforms whose expression profile is often cancer specific. Alternative splicing is known to take place in the mRNA of genes that code for proteins involved in neuronal development and the creation of new nerve fibers. The change in alternative splicing patterns that occur as tumors develop and progress may make these splice variants potential targets for the development of drug treatments. They may also serve as diagnostic or prognostic biomarkers.

Abstract

During development, as tissues expand and grow, they require circulatory, lymphatic, and nervous system expansion for proper function and support. Similarly, as tumors arise and develop, they also require the expansion of these systems to support them. While the contribution of blood and lymphatic systems to the development and progression of cancer is well known and is targeted with anticancer drugs, the contribution of the nervous system is less well studied and understood. Recent studies have shown that the interaction between neurons and a tumor are bilateral and promote metastasis on one hand, and the formation of new nerve structures (neoneurogenesis) on the other. Substances such as neurotransmitters and neurotrophins being the main actors in such interplay, it seems reasonable to expect that alternative splicing and the different populations of protein isoforms can affect tumor-derived neurogenesis. Here, we report the different, documented ways in which neurons contribute to the development and progression of cancer and investigate what is currently known regarding cancer-neuronal interaction in several specific cancer types. Furthermore, we discuss the incidence of alternative splicing that have been identified as playing a role in tumor-induced neoneurogenesis, cancer development and progression. Several examples of changes in alternative splicing that give rise to different isoforms in nerve tissue that support cancer progression, growth and development have also been investigated. Finally, we discuss the potential of our knowledge in alternative splicing to improve tumor diagnosis and treatment.

Nerves in cancer

The contribution of nerves to the pathogenesis of malignancies has emerged as an important component of the tumour microenvironment. Recent studies have shown that peripheral nerves (sympathetic, parasympathetic and sensory) interact with tumour and stromal cells to promote the initiation and progression of a variety of solid and haematological malignancies. Furthermore, new evidence suggests that cancers may reactivate nerve-dependent developmental and regenerative processes to promote their growth and survival. Here we review emerging concepts and discuss the therapeutic implications of manipulating nerves and neural signalling for the prevention and treatment of cancer.

Estrogen increases calcitonin gene-related peptide-immunoreactive sensory innervation of rat mammary gland

Estrogen plays important roles in preparing mammary tissue for lactation. However, estrogen also influences innervation in some tissues. We examined the effect of estrogen on peripheral innervation of mammary tissues of ovariectomized adult virgin female rats. Seven days after ovariectomy, 17beta-estradiol or placebo pellets were implanted subcutaneously, and tissues were harvested 1 week later. Estrogen treatment decreased mammary gland mass and adipocyte content, while ductal content increased and vascular composition was unaffected. Estrogen increased total areas occupied by nerves in mammary gland sections immunostained for the pan-neuronal marker protein gene product 9.5, and this increase persisted after normalizing for treatment-induced differences in gland mass. Although a significant increase in tyrosine hydroxylase-immunoreactive sympathetic nerve area was observed, no difference was detected following correction for differences in gland size, implying a conserved number of sympathetic nerves in the face of reduced gland volume. Calcitonin gene-related peptide-immunoreactive sensory nerve sectional area was also increased, and corrected nerve area remained 88% greater, indicating nerve proliferation during estrogen treatment. Total, sensory, and sympathetic innervation of the nipple and adjacent dermal tissue were unaffected by estrogen. We conclude that chronic estrogen elevation induces selective proliferation of rat mammary gland calcitonin gene-related peptide-containing nerves, which are associated primarily with blood vessels and are probably nociceptors. Because they are likely to subserve a vasodilatory function, increased innervation may promote increased blood flow necessary for milk formation during suckling. Moreover, these findings may help explain abundant anecdotal reports of increased breast sensitivity in humans under high estrogen conditions.

Transneuronal labelling of nerve cells in the CNS of female rat from the mammary gland by viral tracing technique

Using the viral transneuronal tracing technique, the cell groups in the CNS transneuronally connected with the female mammary gland were detected. Lactating and non-lactating female rats were infected with pseudorabies virus injected into the mammary gland. The other group of animals was subjected to virus injection into the skin of the back. Four days after virus injection, infected neurons detected by immunocytochemistry, were present in the dorsal root ganglia ipsilateral to inoculation and in the intermediolateral cell column of the spinal cord. In addition, a few labelled cells could be detected in the dorsal horn and in the central autonomic nucleus (lamina X) of the spinal cord. At this survival time several brain stem nuclei including the A5 noradrenergic cell group, the caudal raphe nuclei (raphe obscurus, raphe pallidus, raphe magnus), the A1/C1 noradrenergic and adrenergic cell group, the nucleus of the solitary tract, the area postrema, the gigantocellular reticular nucleus, and the locus coeruleus contained virus-infected neurons. In some animals, additional cell groups, among others the periaqueductal gray and the red nucleus displayed labelling. In the diencephalon, a significant number of virus-infected neurons could be detected in the hypothalamic paraventricular nucleus. In most cases, virus-labelled neurons were present also in the lateral hypothalamus, in the retrochiasmatic area, and in the anterior hypothalamus. In the telencephalon, in some animals a few virus-infected neurons could be found in the preoptic area, in the bed nucleus of the stria terminalis, in the central amygdala, and in the somatosensory cortex. At the longer (5 days) survival time each cell group mentioned displayed immunopositive neurons, and the number of infected cells increased. The pattern of labelling was similar in animals subjected to virus inoculation into the mammary gland and into the skin. The distribution and density of labelling was similar in lactating and non-lactating rats. The present findings provide the first morphological data on the localization of CNS structures connected with the preganglionic neurons of the sympathetic motor system innervating the mammary gland. It may be assumed that the structures found virus-infected belong to the neuronal circuitry involved in the control of the sympathetic motor innervation of the mammary gland.

Regulation of blood flow in the mammary microvasculature

Although milk yield of cows and goats is known to be closely related to the total flow of blood through the udder, a number of studies suggest that milk yield can vary independently. No studies have attempted to measure the proportion of total flow that is nutritive. Within the mammary gland, capillary networks form a basket-like architecture surrounding each alveolus. Notably, flow in individual capillaries is not constant and varies among capillaries. Capillary flow (measured by intravital microscopy) was decreased by oxytocin, which generally increased total flow in the mammary artery, suggesting that the proportion of total flow that is nutritive can vary. In addition to classic metabolic regulators (e.g., carbon dioxide and oxygen) of tissue blood flow, the mammary gland produces a number of vasodilatory compounds, including parathyroid hormone-related protein, insulin-like growth factor-I, prostacyclin, nitric oxide, and endothelin. All of these compounds have been shown to alter mammary blood flow. Mammary tissue also contains kallikrein and angiotensin-converting enzyme, which convert circulating kinins and angiotensin, respectively, into potent vasoactive compounds. A number of these compounds are produced by epithelial cells themselves, providing a mechanism for the functioning epithelium to control its own blood supply and, hence, nutrient flow for milk synthesis. In this review, we examine the nature of the mammary microcirculation, its behavior under different conditions, and some of the regulatory features of the mammary microvasculature.

Evidence for the involvement of a gastrointestinal peptide in the regulation of glucose uptake in the mammary gland of the lactating rat

1. A method of obtaining serial arterial and mammary-venous blood samples was used to identify possible factors involved in the regulation of glucose uptake in the gland of the lactating rat. 2. Administration of insulin alone increased the arteriovenous glucose difference across the mammary gland of starved rats, but the time course of the recovery could not account for the restoration of arteriovenous glucose difference observed during refeeding [Page & Kuhn (1986). Biochem. J. 239, 269-274]. 3. A crude extract of the gastrointestinal tract (stomach-ileum) from lactating rats enhanced the change in mammary glucose uptake observed with insulin, but only when large amounts (100 munits/rat) of insulin were used. To achieve a similar recovery of arteriovenous glucose difference using near-physiological amounts (5 munits/rat) of insulin it was necessary to sever the mammary nerves. 4. A peptide fraction (of less than 10 kDa) isolated from the gut extract enhanced the effect of insulin in a similar manner to the crude extract. 5. It is suggested that in addition to insulin at least another component, probably a gut peptide, is required for the restoration of mammary glucose uptake during refeeding. An inhibitory component may also contribute to the regulation of mammary glucose extraction in the lactating rat.

Effect of serotonin on the motility of smooth muscles in teats of lactating cows

The effects of serotonin, injected into one udder artery, on teat smooth muscle function were investigated in four lactating cows. Motility of longitudinal smooth muscles was recorded by a plethysmographic technique, and sphincter function by measuring milk leakage from the full udder. Serotonin (40, 120 and 360 micrograms) activated teat muscle tonicity and reduced the volume of milk leakage. The effects on longitudinal smooth muscles were reduced by mianserin and ketanserin (0.375, 1.5 and 6 mg) and by methysergide (1.5 mg). These blocking substances were also effective (0.2, 0.6 and 1.8 mg respectively) in antagonizing the inhibiting action of serotonin on milk leakage. It is suggested that serotonin effects are mediated by receptors of the S2-type.

Substance P immunoreactivity in the rat mammary nipple and the effects of capsaicin treatment on lactation

Tissue concentrations of substance P immunoreactivity (SP-I) were measured in rat mammary nipples and were significantly greater than in ventral abdominal skin in nonpregnant and pregnant rats. In contrast, the concentration of nipple SP-I was lower than that of skin in twelve day lactating animals. The mean total SP-I content of the pooled twelve nipples from each rat was not significantly different in nonpregnant, pregnant or lactating rats. However, the mean weight of the pooled twelve nipples from each rat was significantly higher in the lactating rats than in pregnant rats. Immunohistochemistry revealed SP-I nerve trunks and single fibers throughout the nipples of lactating rats. Nerve fibers were observed among smooth muscle and along blood vessels throughout the dermis and in association with epidermal structures. Some SP-I fibers were also observed in association with the main lactiferous duct and mammary gland secretory parenchyma. Radioimmunoassay and immunohistochemistry of nipples from lactating rats treated with capsaicin as neonates revealed a marked depletion of SP-I. Rats treated with capsaicin as neonates had a normal gestation period and produced litters of normal size and birth weight. However, the litters of these lactating rats grew at a significantly slower rate than litters from controls. The quantity of milk obtained from capsaicin-treated lactating dams, following a one hour suckling period on the twelfth day of lactation, was significantly less than that obtained by litters of control dams. It is concluded that capsaicin-sensitive primary sensory nerves of the mammary nipple play a role in the afferent limb of the suckling reflex. One transmitter candidate for these nerves is substance P.

Is oxytocin really necessary for efficient milk removal in dairy cows?

This review examines the potential importance of mechanisms other than the release of oxytocin for efficient milk removal. First, evidence is presented that oxytocin release is not always essential for efficient milk removal. Second, potential roles for the release of oxytocin during suckling or milking not directly related to milk removal are discussed. Third, alternative mechanisms that potentiate or induce milk ejection are introduced. Finally, the role of the autonomic nervous system in the milk removal process is examined.

Species variation in the distribution of cholinesterases in the ovary of the plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer

Sections of ovary from plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer have been histochemically processed to demonstrate acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in nervous and non-nervous tissue. The effects of different reproductive states on enzyme activity were observed in some animals. AChE-containing nerves were sparse in rabbit and rat but plentiful in cat and roe deer. Nerves containing BuChE were not detectable in ferret or guinea-pig and were rare in cat. Species variations in the activity and type of enzyme were also found in non-neuronal tissues. Some blood vessels in the ovaries of guinea-pig and viscacha contained AChE. No other species showed a reaction for AChE in non-neuronal stromal tissue but BuChE was present at this site in all animals except rat. Granulosa cells reacted for AChE only in cat and rabbit while luteal cells were reactive in cat, rabbit and roe deer. Some BuChE activity was present in granulosa and or luteal cells in all species except roe deer. In rat, BuChE activity in luteal cells increased during pregnancy and the early phase of pseudopregnancy. The difficulty of assigning a function to ovarian cholinesterases is discussed.

Simultaneous demonstration of cholinesterases and glyoxylic acid-induced fluorescence of catecholamines in stretch preparations

A combined simultaneous method to demonstrate adrenergic nerves using glyoxylic acid-induced fluorescence and nerves showing cholinesterase activity using the thiocholine technique is described in whole-mount preparations. The subcutaneous fascia and the right atrium of the heart of the rat and guinea-pig were used as tissue specimens, and the innervation patterns of adrenergic and cholinergic nerves were demonstrated in UV and transmitted light. Technical points and the limitations of the method are discussed.